A blood testosterone test measures the amount of the hormone in a blood sample. Though known as a male sex hormone, testosterone is produced by both males and females. In males, it is produced in the testicles and is responsible for developing male sex organs, sperm production, muscle mass, and a deeper voice. In females, the ovaries and adrenal glands produce smaller amounts that contribute to hormonal balance.
Common Reasons for a Testosterone Test
A doctor may order a testosterone test for symptoms that suggest a hormonal imbalance. For men, the most common reason is to investigate symptoms of low testosterone (hypogonadism), which can include persistent fatigue, a reduced sex drive, erectile dysfunction, and loss of muscle mass. Other indicators might include mood changes, thinning bones, or difficulty fathering a child due to diminished sperm production.
Women are also tested for abnormal testosterone levels, often to help diagnose conditions like Polycystic Ovary Syndrome (PCOS), which is associated with elevated testosterone. Symptoms that might prompt a test for a woman include irregular menstrual periods, difficulty becoming pregnant, or developing masculine features like excess body hair or a deepening voice. In some cases, the test may also be used to investigate tumors on the ovaries or adrenal glands.
The Blood Test Procedure
The process for a testosterone test is a simple blood draw from a vein in the arm. A healthcare professional collects a small blood sample in a test tube, which is then sent to a laboratory for analysis.
The test is almost always scheduled for the morning, between 7 a.m. and 10 a.m. This timing is important because testosterone levels follow a daily cycle, peaking in the early morning and declining throughout the day. A morning blood draw provides the most accurate measurement of peak testosterone production. Your doctor will provide specific instructions regarding fasting.
Understanding Testosterone Levels
Your results will show a value for “total testosterone,” measured in nanograms per deciliter (ng/dL). This number represents all the testosterone in your bloodstream, including testosterone that is attached to proteins and “free” testosterone. For adult men, an accepted normal range for total testosterone is 300 to 1,000 ng/dL, while for women, the normal range is much lower at 15 to 70 ng/dL. It is important to note that these ranges can vary slightly between different laboratories.
Your doctor might also look at “free testosterone,” which is the testosterone not bound to proteins and is readily available for your body’s tissues to use. While total testosterone provides a good overall picture, free testosterone can offer more specific insights, especially if total levels are borderline. Only a small fraction, typically 1-3%, of testosterone is free, but it is the biologically active portion. A low free testosterone level, even with a normal total testosterone, can sometimes explain symptoms of deficiency.
Factors That Affect Testosterone Readings
A single testosterone test result is a snapshot in time and can be influenced by a number of physiological and lifestyle variables. One of the most significant factors is age, as testosterone levels in men naturally begin to decline starting around age 30. This gradual decrease is a normal part of the aging process, though the rate of decline varies between individuals.
Beyond age, daily habits and overall health can have a substantial impact on testosterone production. Other factors that can contribute to lower readings include:
- Chronic stress, which elevates the hormone cortisol
- Insufficient or poor-quality sleep
- Obesity
- Chronic illnesses, such as diabetes
- Use of certain medications